THE STRUCTURE OF NO ON NI(111) AT LOW-COVERAGE

Scanned-energy mode photoelectron diffraction from the N 1s and O 1s c ore levels has been used to determine the local adsorption geometry of NO on Ni(111) at a coverage of 0.25 ML. The optimum surface geometry consists of NO molecules adsorbed in both the fee and hcp three-fold h ollow sites in a ratio of approximately 50/50 (the fee site occupation is 50(-20 /+ 17)% for the N 1s data, and 47(-30/+25)% for the O 1s da ta). N-Ni bond lengths are almost identical for the two sites: 1.83 +/ - 0.07 Angstrom (fcc) and 1.85 +/- 0.07 Angstrom (hsp). We conclude th at for NO adsorption on Ni(lll), the fee and hcp sites are energetical ly similar. (C) 1998 Elsevier Science B.V. All rights reserved.